Raman scattering and the ferroelectric phase transition in 5PbO.3GeO2

The Raman spectrum of the ferroelectric 5PbO.3GeO2 has been recorded at various temperatures. A 'soft' phonon mode associated with the phase transition, which interacts with other modes, was observed and the spectra are analysed in terms of a response function for coupled modes. The variation of the frequency and width of the ferroelectric mode with temperature does not agree completely with conventional theory.